1. Field of the Invention
The invention relates to an apparatus as a component of a video centering system for determining the distance between pupils for precisely defining parameters relevant to the grinding of lenses to be mounted in the sockets of spectacles or eyeglasses.
2. The Prior Art
It is generally known that video systems are utilized for determining parameters relevant to grinding lenses of spectacles which are based upon producing a video photograph of a patient who is wearing the adjusted or fitted frame of his spectacles.
Thus, German patent specification DE 43 23 384 C2 describes a device for measuring the parameters requisite for conforming optical lenses to the frame of spectacles, particularly the distance between the pupils and the height of a person's pupils relative to the spectacle frame. The device is provided with a camera for taking a photograph of the head of the person wearing the spectacle frame and for adjustment with respect to the head. Furthermore, the device is provided with an electronic imaging unit for defining the parameters from the photograph of the head at a predetermined measured distance between the head and the camera. Within the camera, there is provided a coincidence range finder with an optical system behind the objective of the camera for separating the photograph into four adjacent images or partial images such that the correct measuring distance is obtained if the images or partial images join into a single image.
This device in essence consists of a camera to be aimed by its operator against a customer or patient with a follow-up optical system for determining the predetermined measured distance on the basis of a coincident distance measurement. Such an arrangement suffers from two disadvantages, however: It involves significant technical complexity to be made, and its manner of operation is such that measurement errors cannot be excluded.
German patent specification DE 100 20 005 A1 discloses an apparatus for, and a method of, defining the centering data for mounting lenses into spectacle frames. It utilizes a camera and a centering rider with a light source which compels a patient to look into a previously determined direction. Measurement data are read from a previously established centering foil, and the preferred light source is a laser pointer.
Another arrangement by which measuring the distance between the pupils of a human eye may be carried out digitally, is disclosed by German patent specification DE 100 05 801 A1. It proposes an examination frame for measuring the distance between the pupils of the patient's eyes. The examination frame consists of a lens support, a device for moving the lens support along the frame in the direction of the patient's nose or temple. In addition, the examination frame is provided with a source of electrical current and metal strips through which the current is flowing. By rotating the lens supports, the level of current flowing through the metal conductor is measured, and the distance between the pupils of the eyes of a given patient may be deduced from the measured current.
Such an arrangement may be said to suffer from the drawback that for the necessary corrective calculations, in particular the convergence or inward rotation of the eyes at a short viewing distance, it relies upon a shooting distance between the patient and the recording camera stored in the given systems data. In the event, the corrective calculations can be correct only to the extent that the stored values of shooting distances are adhered to during the exposures.